Study finds milk may be harmful

A new study into A1 and A2 milk could have profound implications for human health research, says one of its authors, after results suggested A1 milk slowed digestion in rats.

Most milk produced in New Zealand is A1 milk, defined by the presence of particular beta-casein proteins. A2 milk contains only the A2 form of beta-casein.

Some scientists think the difference may influence human health, particularly the incidence of type-2 diabetes, although the issue has yet to be properly studied.

But research published in March by scientists from AgResearch, Massey and Lincoln Universities found a statistically significant effect on the digestion of rats fed diets of A1 or A2 milk.

The A1 diet slowed the movement of food through the intestine in a manner apparently linked to opioid receptors, researchers found.

Lincoln University professor Keith Woodford, a co-author of the study published in the International Journal of Food Sciences and Nutrition, said the result was consistent with "existing observational evidence that A1 is associated with digestive discomfort, bloating, and constipation relative to A2."

The opioid mechanism was known to be a factor in human digestion – "people on high doses of codeine get constipated."

More promisingly, a raised level of the enzyme dipeptidyl peptidase-4 in the A1 rats could be important in the study of diabetes, said Woodford.

High levels of DPP4 affect glucose metabolism, so A2 milk could be a useful tool in managing diabetes, he said.

"This is something that now needs to be taken seriously.

"We should be urgently setting up human trials to look at this in more detail."

The rat study was particularly significant because previous human population studies had indicated A1 milk was correlated with some health effects.

Fonterra chief technology officer Jeremy Hill, himself involved in research in the 1990s into A1 milk and diabetes, said the study's authors made some interesting observations, "but it is important these claims are validated in controlled human trials.''

Isabel MacNeill of Dairy Australia, an industry-funded organisation working on dairy investment and research projects, said the NZ study was not significant.

"It's not indicative of anything that would come out of a human trial," she said. "Overall it's a weak study with not a great methodology."

Woodford said the established dairy industry saw A2 milk as a threat and would try to discredit the research.

"When there are commercial issues at stake the battle doesn't stay clean."

The research was funded jointly by the New Zealand government and A2 Milk, an NZX listed company which owns intellectual property rights around A2 milk research and marketing.

In February A2 announced sales of $54 million for the six months to December, generating a net profit of $0.6m. Almost all the company's sales were in Australia, where the brand was estimated to have an 8 per cent market share in the grocery sector in December.